Ignition system for a multicylinder engine

ABSTRACT

An ignition system for a multicylinder engine comprising a magneto having an igniting exciter coil to induce an AC voltage in synchronism with rotation of the engine; ignition coils having secondary coil portions respectively connected to ignition plugs for cylinders of the engine, to supply a high voltage to the respective ignition plugs; and a primary current controlling semiconductor switch connected to the igniting exciter coil in parallel therewith to be turned on in advance of respective igniting positions of the cylinders so that a current flows through the semiconductor switch. The ignition system further comprises a signal generator driven by the engine and having signal coils to generate timing signals at the respective igniting positions of the cylinders; and primary current conducting semiconductor switches provided between the respective primary coil portions of the ignition coils and the igniting exciter coil to be turned on by the respective timing signals from the signal generator to abruptly pass the primary current through the respective primary coil portions of the ignition coils whereby a high voltage is established across the secondary coil portions of the ignition coils to spark the ignition plugs.

BACKGROUND OF THE INVENTION

An ignition system for a multiplecylinder engine which uses a battery asan ignition power supply is required to include a distributor whichdistributes a primary current to respective primary coil portions ofignition coils. Such an ignition system, however, has a disadvantagethat the distributor tends to break down due to leakage of water intothe distributor or other causes.

In order to eliminate such a disadvantage, there has been employed suchas ignition system for a multicylinder engine that a magneto is used asan igniting power supply. In the prior art, this ignition systemcomprises a combination of ignition circuits provided individually forthe respective cylinders of the engine. Therefore, the whole ignitionsystem is large-sized and very complicated, which makes the ignitionsystem expensive.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the invention to provide anignition system for a multicylinder engine which does not employ adistributor which is easy to break down, and which requires lessmaintenance.

It is another object of the invention to provide an ignition system fora multicylinder engine which is small-sized, simple in its constructionand therefore inexpensive.

It is further object of the invention to provide an ignition systemwherein a spark performance of the ignition system is not lowered.

In accordance with the invention, there is provided an ignition systemfor multicylinder engine comprising a magneto having an exciter coil toinduce an AC voltage in synchronism with rotation of an engine; ignitioncoils having primary coil portions connected to the magneto andsecondary coil portions connected to ignition plugs for cylinders of theengine, respectively, to supply a high voltage to the plugs; a primarycurrent controlling semiconductor switch connected to the magneto inparallel therewith to be turned on in advance of the respective ignitingpositions of the cylinders so that a current flows through the primarycurrent controlling semiconductor switch; a signal generator driven bythe engine and having signal coils to generate timing signals at therespective igniting positions of the cylinders; and primary currentconducting semiconductor switches provided between the respectiveprimary coil portions of the ignition coils and the magneto and adaptedto be turned on by the respective timing signals from the signalgenerator to abruptly pass the primary current through the respectiveprimary coil portions of the ignition coils whereby a high voltage isestablished across the secondary coil portions of the ignition coils tospark the corresponding ignition plugs.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the invention will beunderstood from the description of the embodiments taken along withreference to the accompanying drawings in which;

FIG. 1 is a schematic diagram of one embodiment of an ignition systemfor a multicylinder engine according to the invention;

FIGS. 2a through 2e illustrate the operation of the portions of theignition system of FIG. 1; and

FIG. 3 is a schematic diagram of another embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to FIG. 1, there is shown an embodiment of an ignitionsystem for a two-cylinder engine. This ignition system comprises amagneto 1 having an igniting exciter coil which induces an AC voltage insynchronism with rotation of the engine.

A primary current controlling semiconductor switch which is in the formof a gate turn-off thyristor 2 (hereinafter referred to as G.T.O.) hasan anode and a cathode connected to both ends of an exciter coil of themagneto 1. The cathode of the G.T.O. 2 is grounded. A series connectionof a resistor 3 and a diode 4, the cathode of which is connected to theresistor 3, is connected to the magneto 1 in parallel with the G.T.O. 2.A capacitor 5 is connected across the anode and cathode of the diode 4.This series connection serves to conduct a current therethrough, whichcurrent is produced by a voltage across the exciter coil of the magnetoin a reverse direction to that of an arrow in FIG. 1.

A first ignition coil 6 has a primary coil portion, one end of which isconnected to the point of connection between the exciter coil of themagneto 1 and the anode of the G.T.O. 2 and the other end of which isconnected to the anode of a primary coil conducting semiconductor switchsuch as a thyristor 7, while the cathode of the thyristor 7 is connectedto the point of connection between the exciter coil of the magneto 1 andthe cathode of the G.T.O. 2. A second ignition coil 8 has a primary coilportion, one end of which is similarly connected to the point ofconnection between the exciter coil of the magneto 1 and the anode ofthe G.T.O. 2 and the other end of which is similarly connected to theanode of a primary coil conducting semiconductor switch such as athyristor 9, while the cathode of the thyristor 9 is connected to thepoint of connection between the exciter coil of the magneto 1 and thecathode of the G.T.O. 2. Thus, it will be noted that the respectiveseries connections of the ignition coils 6 and 8 and the thyristors 7and 9 are connected to the exciter coil of the magneto 1 in parallelwith the G.T.O. 2 and with each other. The ignition coils 6 and 8 haverespective secondary coil portions which are connected in series withignition plugs 10 and 11 in two cylinders of the engine.

There is provided a signal generator including two signal coils 14 and17 for the respective cylinders of the engine, which is driven by theengine to generate timing signals at the respective igniting positionsof the cylinders. The signal coils at one end are grounded and at theother end connected through resistors 13 and 16 to the gates of thethyristors 7 and 9, respectively, which gates are also connected throughresistors 12 and 15 to the respective cathodes of the thyristors 7 and9. The signal coils 14 and 17 at the one end are also connected to theanodes of diodes 18 and 19, respectively, the cathodes of which areconnected to each other so as to form an OR gate.

There is also provided control means for controlling the gate of theG.T.O. 2, which comprises a coil 23 of a pulser. The pulser at one endis grounded and at the other end connected to the anodes of diodes 22and 24, the cathodes of which are connected through a resistor 21 and acapacitor 25 to the gate of the G.T.O. 2 respectively. A resistor 20 isalso connected across the gate and cathode of the G.T.O. 2.

An auxiliary thyristor 26 has the anode connected between the point ofconnection between the diode 24 and the capacitor 25, the cathode of theauxiliary thyristor 26 being grounded and the gate of the thyristor 26being connected through a resistor 27 to the cathode thereof and alsoconnected to the output of the OR gate or the cathodes of the diodes 18and 19.

In operation, as the exciter coil 1 begins to induce a forward voltagein a direction of a solid arrow in FIG. 1 from the point of θ_(a) inFIG. 2, the pulser coil 23 concurrently induces a forward voltage in adirection of an arrow in FIG. 1, which causes a firing signal to beapplied through the diode 22 and the resistor 21 to the gate of theG.T.O. 2. Accordingly, the G.T.O. 2 is turned on, and as a result ananode current flows through the G.T.O. 2 from the point of θ_(a) asshown in FIG. 2a. At that time, the capacitor 25 is charged through thediode 24 so that the cathode of the diode 24 is at a positive potentialwhile the gate of the G.T.O. 2 is at a negative potential. At theigniting position θ₁ of the first cylinder, the signal coil 14 for thefirst cylinder generates an igniting signal as shown in FIG. 2d, whichis applied through the resistor 13 to the gate of the thyristor 7. Thiscauses the thyristor 7 to be turned on. At the same time, the ignitingsignal is also applied through the diode 18 to the gate of the thyristor26. This causes the thyristor 26 to be turned on. Thus, the capacitor 25is discharged through the anode and cathode of the thyristor 26 and thenthrough the cathode and gate of the G.T.O. 2. As a result, the G.T.O. 2is turned off, and therefore, the anode current of the G.T.O. 2 isabruptly interrupted as shown in FIG. 2a. Because of such an abruptchange in the current, the exciter coil of the magneto 1 induces a highvoltage thereacross. Since the thyristor 7 is in the conductivecondition at that time, a large primary current abruptly flows throughthe primary coil portion of the ignition coil 6 for the first cylinder.Thus, the ignition coil 6 generates a high voltage across the secondarycoil portion thereof, by which the ignition plug 10 in the firstcylinder is spark-discharged to ignite or explode the first cylinder. Itshould be noted that the igniting signal from the signal coil 14 is notapplied to the gate of the thyristor 9 because the diode 19 blocks thesignal from the signal coil 14.

At the igniting position θ₂ of the second cylinder, the anode current ofthe G.T.O. 2 which flows from the point θ_(b) in advance of the pointθ₂, is abruptly interrupted as shown in FIG. 2a, when the auxiliarythyristor 26 is turned on by the firing signal from the signal coil 17for the second cylinder. At that time, the thyristor 9 is in theconductive condition, and as a result a large primary current flowsthrough the primary coil portion of the ignition coil 8 for the secondcylinder as shown in FIG. 2c. Thus, the ignition coil 9 generates a highvoltage across the secondary coil portion thereof, by which the ignitionplug 11 is spark-discharged to explode the second cylinder.

FIG. 3 shows another embodiment of the ignition system for themulticylinder engine. This is substantially identical to the embodimentof FIG. 1, except that the primary current controlling semiconductorswitch comprises a transistor 28 in place of the G.T.O. 2 of theaforementioned embodiment. The collector and emitter of the transistor28 are connected to both ends of the exciter coil of the magneto 1 withthe emitter being grounded, while the base of the transistor 28 isconnected through a resistor 29 to the collector of the transistor 28and also to the anode of the thyristor 26. Also, in this embodiment, thepulser 23, the diodes 22 and 24, the resistor 21 and the capacitor 24 ofFIG. 1 are not required. The operation of the ignition system of FIG. 3is also identical to that of FIG. 1, but the transistor 28 which isnormally conductive, is turned off when the thyristor 26 is turned on bythe signals from the signal coils 14 and 17 of the signal generator, sothat the primary current flows through the primary coil portion of theignition coil 6 or 8.

It will be understood that the invention can be applicable to an enginehaving three, four, six and more cylinders in a similar manner. In thesecases, the number of the ignition coils, the ignition plugs, the primarycurrent conducting semiconductor switches, the signal coils of thesignal generator and the diodes to output the signals from the signalcoils should be increased in correspondence to the number of thecylinders.

It will be noted that two ignition plugs may be connected to each of thesecondary coil portions of the ignition coils 6 and 8 so that theignition plugs are provided at both ends of the secondary coil portionsin a symmetrical manner. In this case, the system can be applied to anengine having twice as many cylinders as ignition coils, but it shouldbe noted that each of the two ignition plugs connected to each ignitioncoil should be provided in each of the two cylinders, one of which is atthe ignition position while the other cylinder is at the end of theexhaust position. Thus, if another ignition plug is provided for each ofthe ignition coils 6 and 8 in the embodiments of FIGS. 1 and 3, it willbe noted that the system may be applied to a four cycle and fourcylinder engine.

Although some embodiments of the invention have been illustrated anddescribed with reference to the accompanying drawings, it will beunderstood by those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe invention, which is intended to be defined only to the appendedclaims.

What is claimed is:
 1. An ignition system for a multicylinder enginecomprising a magneto having an igniting exciter coil to induce an ACvoltage in synchronism with rotation of the engine;ignition coils eachhaving a primary coil portion and a secondary coil portion connected toan ignition plug for each cylinder of said engine to supply a highvoltage across said ignition plug; a primary current controllingsemiconductor switch connected in parallel with said igniting excitercoil; a control circuit to control said primary current controllingsemiconductor switch so that the primary current controllingsemiconductor switch is turned on in advance of each igniting positionof the respective cylinders and is turned off when a timing signal isapplied to the control circuit; a signal generating means driven by saidengine and having signal coils which generate the timing signals at saidrespective igniting positions of the cylinders; primary currentconducting semiconductor switches corresponding to said ignition coilsand connected in series with the respective primary coil portions of theignition coils, the respective series connections of the primary coilportions and the primary current conducting semiconductor switches beingconnected in parallel with said igniting exciter coil; said signal coilsbeing coupled to the respective primary current conducting semiconductorswitches so that the respective primary current conducting semiconductorswitches are turned on by the respective timing signals; and said signalcoils being further coupled to said control circuit to supply the timingsignals thereto; whereby said primary current controlling semiconductorswitch is turned off at the same time as said primary current conductingsemiconductor switches are turned on at the respective ignitingpositions of the cylinders and a high voltage is established across saidsecondary coil portions of said ignition coils to spark thecorresponding ignition plugs.
 2. An ignition system for a multicylinderengine as set forth in claim 1, wherein said primary current controllingsemiconductor switch comprises a gate turn-off thyristor, and saidcontrol circuit comprises a pulser coil to supply a firing signal to agate of said gate turn-off thyristor in advance of the respectiveigniting positions of said cylinders, a capacitor connected to becharged by said pulser coil, and an auxiliary thyristor connected toreceive the respective timing signals from said signal generating means,said capacitor being discharged through said auxiliary thyristor andthen a cathode and gate of said gate turn-off thyristor to turn off saidgate turn-off thyristor.
 3. An ignition system for a multicylinderengine as set forth in claim 2, and further comprising an OR gateprovided between said signal coils of said signal generating means and agate of said auxiliary thyristor.
 4. An ignition system for amulticylinder engine as set forth in claim 3, wherein said OR gatecomprises diodes each having an anode connected to a correspondingsignal coil of said signal generating means and a cathode connected tothe gate of said auxiliary thyristor.
 5. An ignition sysbem for amulticylinder engine as set forth in claim 1, wherein said primarycurrent controlling semiconductor switch comprises a transistor, saidcontrol circuit comprises means to supply a turn-on current from saidigniting exciter coil to a base of the transistor in advance of therespective igniting positions of said cylinders, and an auxiliarythyristor connected to said transistor so that said transistor is turnedoff when said auxiliary thyristor is turned on, and said timing signalsbeing applied to a gate of said auxiliary thyristor to turn on saidauxiliary thyristor.
 6. An ignition system for a multicylinder engine asset forth in claim 5, wherein said means to supply a turn-on currentfrom said exciter coil comprises a resistor connected between acollector and a base of said transistor.
 7. An ignition system for amulticylinder engine as set forth in claim 5, and further comprising anOR gate provided between said signal coils of said signal generatingmeans and the gate of said auxiliary thyristor.
 8. An ignition systemfor a multicylinder engine as set forth in claim 7, wherein said OR gatecomprises diodes each having an anode connected to a correspondingsignal coil of said signal generating means and a cathode connected tothe gate of said auxiliary thyristor.